Interior Ballistic Evaluation of High-Flame Temperature Propellants in 20mm Ammunition and Assessment as an Erosion Test Device
ARMY BALLISTIC RESEARCH LAB ABERDEEN PROVING GROUND MD
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Gun barrel wear tests have uncovered the need for a small scale device to test barrel treatments like thick chromium. Small caliber barrels have traditionally served this role, but results with high-firing rates used to produce measurable wear are ambiguous. An ideal erosion test device would be a small caliber gun with standard projectiles, cartridge cases and propellants which would produce wear comparable to wear in large-caliber guns. Interior ballistic tests were done with M2 or M9 propellant in place of the standard ball powder in the M55A2TP-T round to determine charge masses which would not exceed the peak chamber pressure of the reference M55A2TP-T round. The wear produced with the high-flame temperature propellants was estimated with the Frankle-Kruse empirical formula. The results showed an M9 propellant could be loaded to the same charge mass as the reference WC870 ball powder with a lower peak chamber pressure but 100 ms higher velocity. The wear estimated for such a round is 5 micrometershot, comparable to wear -limited Army guns, but less than the desired 25 micrometershot 1 milshot for an erosion test device. Hence the 20-mm gun with M9 propellant could be useful for evaluating chromium-plating for existing guns, but it has too little wear for conveniently assessing future platings and coatings.